Chemistry · Class 11 · Equilibrium

Chemical Equilibrium for JEE

Everything you need for this topic on one page: the ideas, the formulas, the traps, and free lectures that explain it well.

Last updated: 26 October 2026

Direct answer

Law of mass action, Kc and Kp, reaction quotient, Le Chatelier's principle and degree of dissociation.

Key ideas

Chemical Equilibrium: what you must understand

At equilibrium forward and backward rates are equal
Q < K: reaction goes forward; Q > K: backward
Only temperature changes the value of K
Pure solids and liquids are not written in K

Formula sheet

Must-know formulas for Chemical Equilibrium

Kp = Kc(RT)^Δn
K for reversed reaction = 1/K; multiplied by n → Kⁿ
ΔG° = −RT ln K
Van 't Hoff: log(K₂/K₁) = ΔH°/(2.303R)(1/T₁ − 1/T₂)

One-page formula sheet

Printable Chemical Equilibrium formula sheet: formulas, key ideas and traps on one page. Save it as a PDF for offline revision.

Avoid

Common mistakes students make

Including solids in K
Thinking pressure or catalysts change K
Wrong Δn in Kp–Kc relation

For the exam

How this topic is asked in JEE

Appears frequently. Le Chatelier and Kp–Kc questions are quick marks.

Prerequisites: Mole Concept and Stoichiometry.

NCERT map

Where Chemical Equilibrium is in NCERT

Chapter names follow the current rationalised NCERT textbooks. Read these sections before solving PYQs.

Class	Book	Chapter	Sections JEE asks from
Class 11	Chemistry Part I	Equilibrium	Law of Chemical Equilibrium and Equilibrium Constant; Homogeneous Equilibria; Relationship between Equilibrium Constant K, Reaction Quotient Q and Gibbs Energy G; Factors Affecting Equilibria

JEE Advanced level

A JEE Advanced-level example on Chemical Equilibrium

Question. PCl5 dissociates as PCl5(g) ⇌ PCl3(g) + Cl2(g). At 250°C, 0.1 mol of PCl5 is placed in a 2L vessel. At equilibrium, the total pressure is 2.46 atm. Find (a) the degree of dissociation, (b) Kp, and (c) the new degree of dissociation if the volume is suddenly halved at constant temperature.

Show solution

At equilibrium: moles of PCl5 = 0.1(1−α), PCl3 = 0.1α, Cl2 = 0.1α. Total moles = 0.1(1+α).
Using PV = nRT: 2.46 × 2 = 0.1(1+α) × 0.0821 × 523. Solving gives α = 0.146 (14.6%).
Kp = α²P/(1−α²) = (0.146)² × 2.46 / (1 − 0.0213) = 0.0535 atm.
When volume is halved, new pressure P' = 4.294(1+α'). Since Kp is constant: 0.0535 = 4.294α'²/(1−α').
Solving the quadratic 4.294α'² + 0.0535α' − 0.0535 = 0 gives α' = 0.106 (10.6%). The decrease confirms Le Chatelier's principle since higher pressure favors fewer moles.

Answer: (a) α = 0.146 or 14.6%, (b) Kp = 0.0535 atm, (c) New α = 0.106 or 10.6%

This example was solved twice independently and both solutions agree.

Free lectures

Best free lectures for Chemical Equilibrium

Full-chapter free lectures picked from YouTube search results by views, from established JEE channels (mostly in Hinglish). Use the subtopic list to jump straight to the part you need (timestamps come from each video's own chapter list). Watch one, then solve PYQs the same day.

Chemical Equilibrium FULL CHAPTER | Class 11th Physical Chemistry | Chapter 5 | Arjuna JEE — Arjuna JEE, 3:41:58
Jump to a subtopic (15)
- 00:00 Introduction
- 05:46 Types of Chemical
- 15:14 Concept of Equilibrium
- 22:44 Physical Equilibrium
- 43:01 Chemical Equilibrium
- 01:24:00 Heterogeneous Equilibria
- 01:27:59 Expression of Equilibrium Constant
- 02:02:39 Characteristics of Equilibrium Constant
- 02:16:03 Effect of Temperature on Equilibrium Constant
- 02:20:41 Application of Equilibrium Constant
- 02:52:09 Relationship Between Keq' Q and G
- 03:03:16 Le Chatelier's Principle
- 03:27:22 Effect on Physical Equilibrium
- 03:33:04 Vapour Density and Degree of Dissociation
- 03:40:05 Thank You Bachoo!!
CHEMICAL EQUILIBRIUM in One Shot: All Concepts & PYQs Covered | JEE Main & Advanced — JEE Wallah, 5:43:07
Jump to a subtopic (16)
- 00:00 Introduction
- 06:50 Types of chemical reactions
- 19:06 Concept of equilibrium
- 31:05 Physical equilibrium
- 1:01:14 Chemical equilibrium
- 1:54:28 Homogeneous and heterogeneous equilibria
- 2:00:14 Expression of equilibrium constant
- 2:34:23 Characteristics of Equilibrium constant
- 3:11:35 Effect of temperature
- 3:18:31 Applications of Equilibrium constant
- 3:34:12 Calculating equilibrium concentrations
- 4:09:30 Relationship between Keq, Q and G
- 4:35:20 Factors affecting equilibria
- 5:13:11 Effect on physical Equilibrium
- 5:32:32 Simultaneous equilibria
- 5:38:36 Thank You Bachhon!

Practise

Where to practise for free

13 JEE Main 2026 PYQs on Chemical Equilibrium, with solutions.
Read the chapter in NCERT textbooks (official, free), then solve its NCERT Exemplar (official, free) questions.
Chapter-wise past questions: JEE Main and Advanced PYQs and question bank.
Timed practice tests: NTA Abhyas practice tests (official, free) and our free mock tests.
See it move: interactive simulation.

FAQs

Frequently asked questions

Is Chemical Equilibrium important for JEE Main 2027?

Appears frequently. It is part of the official 'Equilibrium' unit in the JEE Main 2027 syllabus.

What are the most important formulas in Chemical Equilibrium?

Kp = Kc(RT)^Δn; K for reversed reaction = 1/K; multiplied by n → Kⁿ; ΔG° = −RT ln K.

How should I study Chemical Equilibrium for JEE?

Understand the key ideas from NCERT or one full lecture, learn the formula sheet, then solve 25–30 past JEE questions on the topic. Le Chatelier and Kp–Kc questions are quick marks.